Landfill gas is produced through the natural anaerobic decomposition of predominantly organic waste material
deposited in a landfill. The quantity and composition of the gas depends on the characteristics of the
waste disposed and the time elapsed after disposal. Typical landfill gas contains about one half methane,
half carbon dioxide with nitrogen and hydrogen sulfide (H2S). (COD Permit 62)
Methane gas is odorless and colorless. The odors come from other constituent gases within the landfill. The
lack of an odor does not mean that methane is not present. Harmful exposure to humans occurs only if the
landfill is producing high levels of gas and if the landfill has no properly function gas collection and control
system, without which gases can migrate from the landfill cover system. However, proper monitoring and
control of landfill gas is necessary because landfill gas is explosive.
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What type of gases can pose explosion hazard?
- Methane gases pose the greatest amount of hazard. Its explosive level is between lower explosive limit
(LEL) of 5% by volume and its upper explosive limits (UEL) of 15% by volume. Methane gases are unlikely to
explode within the landfill, because concentrations within the waste mass are usually 50% (much higher than its UEL).
- Other landfill gases such as ammonia and hydrogen sulfide are flammable but are unlikely to be present at
concentrations above their LEL.
Although landfill gas explosions are not common, a number of incidents have been attributed to landfill gas:
1999 |
An 8 year-old girl was burned on her arms and legs while playing on an Atlanta Playground. The area was reportedly used as an illegal dumping ground many years ago. (Atlanta Journal-Constitution 1999) |
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1994 |
While playing soccer in a park built over an old landfill in Charlotte, North Carolina, a woman was seriously burned by a methane explosion (Charlotte Observer 1994). |
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1987 |
Off-site gas migration is suspected to have caused a house to explode in Pittsburgh, Pennsylvania. (EPA 1991) |
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1984 |
Landfill gas migrated to and destroyed one house near a landfill in Akron, Ohio. Ten houses were temporarily evacuated. (EPA 1991) |
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1983 |
An explosion destroyed a residence across the street from a landfill in Cincinnati, Ohio. Minor injuries were reported. (EPA 1991) |
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1975 |
In Sheridan, Colorado, landfill gas accumulated in a storm drainpipe that ran through a landfill. An explosion occurred when several children playing in the pipe lit a candle resulting in serious injury to all the children. (USACE 1984) |
Many people find that odors from a landfill are unpleasant. Some may experience nausea or headaches, but this only occurs if the individual is exposed to high levels of the odors associated with the gases. In most cases, medical attention is not necessary.
Here are a few do's and don'ts given to us by City of Dallas, Landfill Manager, Rick White:
- Never smoke or create an open flame or spark near a landfill gas source, like a landfill gas extraction well or leachate riser. Use signage to identify these hazard areas and to direct proper caution.
- Landfill gas can also escape through cracks or highly permeable areas in the cover of a landfill. Seal open cracks in the landfill cover periodically.
- When the job requires long-term exposure to landfill gas sources (i.e. gas extraction wells), use a respirator approved to filter gases. Take frequent breaks in well-ventilated areas away from the gas source. The air that's just a short distance away from the source will be greatly diluted with oxygen.
- Always have a partner present when opening or working on landfill gas sources like gas extraction wells and leachate risers to assist you in the event that the fumes overcome you.
- Use proper ventilation devices to evacuate any accumulations of gas when entering a confined space near a landfill gas source. Some landfills employ buried vaults for various purposes. Drainage culverts can be confined spaces that contain landfill gas. Use a gas detection device to determine if harmful levels of gas are present, prior to entering a work area.
- Periodically, check for methane and other gases inside buildings located near gas sources.
- Make sure all buildings are well ventilated.
- Typically, gas enters a building through the plumbing system or an opening in the floor or foundation. The
gas is intercepted by the gravel pack around the sewer or water line and follows its path back to the
building. Crawl spaces under raised buildings should also be well ventilated.
Atlanta Journal-Constitution. (1999) "Mysterious gas blast closes park"; February 9, 1999.
Charlotte Observer. (1994) Women severely burned playing soccer. November 7, 1994.
EPA. Integrated Risk Information System (IRIS). http://www.epa.gov/iris.
City of Dallas Department of Sanitation. Landfill Permit 62 (sec. 1.1)